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Asked: 2026-05-10T13:59:35+00:00

How do you specify that a foreign key constraint should be a 1:1 relationship

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How do you specify that a foreign key constraint should be a 1:1 relationship in transact sql? Is declaring the column UNIQUE enough? Below is my existing code.!

CREATE TABLE [dbo].MyTable(     [MyTablekey] INT IDENTITY(1,1) NOT FOR REPLICATION NOT NULL,     [OtherTableKey] INT NOT NULL UNIQUE         CONSTRAINT [FK_MyTable_OtherTable] FOREIGN KEY REFERENCES [dbo].[OtherTable]([OtherTableKey]),     ...     CONSTRAINT [PK_MyTable] PRIMARY KEY CLUSTERED      (         [MyTableKey] ASC     ) WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY] ) ON [PRIMARY] GO
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  1. A foreign key column with the UNIQUE and NOT NULL constraints that references a UNIQUE, NOT NULL column in another table creates a 1:(0|1) relationship, which is probably what you want.

    If there was a true 1:1 relationship, every record in the first table would have a corresponding record in the second table and vice-versa. In that case, you would probably just want to make one table (unless you needed some strange storage optimization).

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